1. Field of the Invention
The present invention relates to traffic overload control in intelligent electronic networks, such as telephone networks.
2. Description of the Related Art
Additional features and functionality provided by telephone networks, for example, are growing at a rapid and largely unpredictable rate. Future new services will provide traffic demands on the network which are difficult to predict and will have demand profiles unlike those of the traditional telephone service. In other words in advanced intelligent networks, multiple services will be contending for the resources of various common network elements. In particular, service control points (SCPs) will form a natural point of concentration of the intelligence embedded in such networks. Numerous papers (see, for example, Franks and Wirth xe2x80x9cUPT traffic issuesxe2x80x94an agenda for the 90""sxe2x80x9d and Lipper and Rumsewicz, xe2x80x9cTraffic issues in Personal Communications Servicexe2x80x9dxe2x80x94both papers published in the proceedings of the 8th ITC Specialist Seminar on Universal Personal Telecommunications, Santa Margherita Ligure, Italy, October, 1992), have argued that traffic on the telephone and signalling network will come much more unpredictable and volatile, with the consequence that overload control becomes a necessity, rather than a luxury, in the networks of the present and future. With numerous services being supported by common platforms, it is critical to build controls or xe2x80x9cfirewallsxe2x80x9d that protect each service from the potentially detrimental impact of sudden load increases in a subset of the supported services. A failure to build effective controls will leave customers (both commercial and residential) unsatisfied. Consequently effective overload control is essential in modern networks to ensure that the network is robust.
The general problems of overload control in intelligent networks are well known and an overview of such problems is found in the article xe2x80x9cOverload control of SCP systemsxe2x80x9d by U. Korner published in xe2x80x9cProceedings of the 13th International Teletraffic Congress, Copenhagen 1991xe2x80x9d.
It is therefore desirable to overcome one or more of the existing problems and to provide a method of, and apparatus for, determining, in real-time, when congestion or overload occurs in an intelligent electronic network.
It is also desirable to control congestion or overload in a telephone network including a service control point (SCP) in a manner which maintains SCP throughput at targeted levels.
According to one aspect of the invention there is provided a method of controlling traffic through at least one node in an intelligent telecommunications network having one or more subsystems that provide subscriber services in response to requests from customers for the services, said method comprising the steps of:
continuously monitoring the moving average of the traffic profile passing through the node for the or each subsystem;
detecting when congestion occurs at the node;
determining from said moving average of the traffic profile whether the congestion is caused by a sudden change in the traffic profile for a particular subsystem; and
invoking congestion controls to control congestion at the node for the particular subsystem in which a sudden change in the traffic profile is determined.
According to another aspect of the invention, there is provided apparatus for controlling traffic in an intelligent telecommunications network having one or more nodes at which subscriber services are provided, wherein the apparatus comprises a service control means connected to the node or nodes and which is arranged to monitor the moving average of the traffic profile of requests for each subscriber service passing through the or each node, and arranged to produce a congestion control signal for a node -when a sudden change in the traffic profile of requests for a particular subscriber service causes congestion at the node.
The service control means preferably includes a central processing unit (CPU) at a service control point (SCP), the CPU being programmed to respond to query messages from nodes or service switching points (SSPs) when requests for subscriber services are received at the switching service points. The CPU may be conveniently programmed to send congestion control signals to the service switching points when it responds to the query messages.
In the method and apparatus of the invention, the moving average of the traffic profile for a particular subsystem or subsystems is preferably monitored by counting means for counting the number of requests for each subscriber service received at the service switching points within predetermined sequential time periods. The CPU of the service control point (SCP) may include means for comparing the number of requests for a particular subscriber service with the total number of requests in each predetermined time period.
The CPU may also include means for calculating an average of the amount of requests for particular subscriber services received over a plurality of preceding predetermined time periods and comparison means for comparing the amount of requests for a particular subscriber service in the most recent or current predetermined time period with said average of the amount of requests for that particular subscriber service in order to determine whether or not a sudden change in the traffic profile for that subscriber service has occurred.
The CPU of the service control point (SCP) preferably includes a database or list of all the subscriber services or dialled numbers available at the service switching points to which the service control point is connected. The CPU is preferably programmed to compile a focus list of dialled numbers of subscriber services which it has determined as a potential focus of congestion which may require congestion control. For instance, when the number of requests for a particular dialled number exceeds a threshold percentage or fraction of the total number of requests processed by the CPU in one of the predetermined time periods (the current monitoring interval), that dialled number may be placed on the focus list of dialled numbers which may require congestion control. Preferably, the CPU is programmed to target a particular dialled number on the focus list for congestion control if the amount of requests for that dialled number in the current monitoring interval is higher than the average amount of requests for that number over a plurality of preceding monitoring intervals.
Preferably, means are provided for determining the processor utilisation of the CPU to determine when congestion exists. This may be used to determine whether a general overload of traffic exists in addition to a focussed overload for a dialled number representing a particular subscriber service, which may be caused by a mass call in for the particular subscriber service.
Any convenient type of congestion control may be utilised in the method and apparatus of the present invention. In one particular embodiment, the SCP/CPU is arranged to send a congestion control signal to a switching service point (SSP) where congestion is detected for a particular subscriber service, and the admission control means is responsive to the congestion control signal to apply congestion control by throttling or limiting the percentage or fraction of queries which are passed by that SSP to the SCP.